Filter apparatus are known for filtering particles in a fluid stream. The filtration operation essentially removes particles of a particular size from the fluid stream to cleanse the fluid stream of contaminants. The filter media typically utilize fine fibers and have the necessary void volume to process increased flows without exhibiting a high pressure drop. The fibers may be made of materials such as, for example, fiberglass, synthetic fibers, or even natural fibers.
As the fluid flows through the filter apparatus, certain liquids such as hydraulic fluids and diesel and gasoline fuels can have resistance to the conductance of electricity. As such, a static charge can build up within the liquid from the action of the non-conductive liquid flowing through the non-conductive filter media. With some of the more advanced compositions of filter media, and with the increasing use of ashless, synthetic, and biodegradable fluids with low conductivity values (i.e., little or no metal additives), static charge can accumulate within the filter apparatus. When the potential between the liquid and a conductive housing component reaches a certain level, a spark can jump to a surface of the housing component. This can be undesirable in many situations.
One technique for removing the static charge in the fluid is to add an anti-static agent such as DuPont Stadis 450 to make the fluid slightly conductive. However, anti-static agents can lose potency over time and will typically have to be re-added (re-doped) to the fluid at regular intervals.
Another technique to removing the static charge has been to introduce a conductive material, e.g., conductive particles or conductive fibers into the filter media along with the non-conductive fibers. Other attempts at solving the build up of static charge include the use of fine stainless steel mesh downstream of the fiberglass media. This approach requires the stainless steel mesh to be grounded to earth to carry away charge (U.S. Pat. No. 6,099,726).